Intraocular lens manufacturing process

ABSTRACT

A method of cast molding an intraocular implant from two or more dissimilar materials using disposable molds. The subject cast molding method is particularly useful in the production of intraocular lenses manufactured from dissimilar materials. It is desirable to produce intraocular lenses from dissimilar materials in order to optimize the optical characteristics of the intraocular lens optic portion and to optimize stability and flexibility characteristics of the intraocular lens haptic elements.

FIELD OF THE INVENTION

The present invention relates to a method of cast molding a surgicalimplant produced from two or more dissimilar materials, implants soproduced and molds useful therefor. More particularly, the presentinvention relates to a method of cast molding intraocular lensesproduced from two or more dissimilar materials using disposable plasticmolds.

BACKGROUND OF THE INVENTION

The use of intraocular lenses (IOLs) to improve vision through thereplacement of damaged or diseased natural lenses or to work inconjunction with a natural lens has obtained wide acceptance since theearly 1980s. Accordingly, a wide variety of IOLs has been developed forsurgical implantation into the posterior and/or anterior chamber of aneye. Commercially available IOLs generally comprise an optic portion andone or more haptic elements or plates to maintain proper positioning ofthe optic portion within the eye. The optic portions of such IOLs arecommonly manufactured from relatively hard or rigid materials such as,for example, polymethylmethacrylate (PMMA), or from relatively soft,resilient polymeric materials such as, for example, hydrogels, acrylicsor silicones. More resilient polymeric materials are advantageous in theproduction of IOLs in that such materials are deformable and foldable toallow for implantation of the IOL through a smaller incision than thatpossible if implanting a more rigid IOL.

To manufacture a biocompatible IOL using known molding techniques, apolished stainless steel mold, having a mold cavity formed in a shape toachieve the desired refraction of light for the particular materialutilized, is first selected. In the case of silicone for example, theuncured silicone polymer is introduced into the mold cavity and thencured. Several methods of molding IOLs are known such as injectionmolding, liquid injection molding, compression molding and transfermolding.

Several significant problems have been associated with known IOL moldingtechniques. The first problem is that current molding processes arelabor intensive. Many elastomers used to mold IOLs, such as for examplesilicone elastomers, often times leave a residue in the stainless steelmolds. Due to this residue, the molds must be cleaned between eachmolding cycle. In addition to being labor intensive, the cleaningrequirements result in significant downtime for the equipment, whichfurther increases production costs. A second problem associated withcurrent known molding techniques is that of frequent tool damage andwear due to the repeated cleanings. Accordingly, molds must be replacedoften resulting in increased production costs. A third problemassociated with such molding techniques is one of quality control withrespect to the molded lenses. Intraocular implants such as IOLs musthave smooth polished edges for implantation within an eye. Improperlyfinished edges on implants may result in damage to interior structuresof the eye. In the case of improperly finished edges on IOLs, abrasionsof the iris and tearing of the trabecular meshwork may result.Unfortunately, steel molds typically leave minute gaps between moldhalves during the molding operation due to construction tolerances.Consequently, material flows out through the gaps during the molding ofthe IOL resulting in a phenomenon known as “flash”. Flash is unwantedmaterial attached at the mold parting line on the molded implant. Thisflash material must be ground and/or polished off the implant, which isagain labor intensive and increases production costs.

SUMMARY OF THE INVENTION

The present invention is a process for cast molding surgical implants,such as but not limited to corneal inlays, shunts and intraocular lenses(IOLs), but most preferably IOLs, wherein in the case of IOLs, the opticportion and haptic elements are produced using two or more dissimilarbiocompatible materials. However, if desired, the subject molds andmolding techniques are likewise useful in the manufacture of surgicalimplants such as in the case of IOLs having an optic portion and hapticelements produced using the same or similar biocompatible materials. Thepresent cast molding process avoids the problems noted with regard toknown molding techniques through the use of disposable plastic molds,which are less expensive and less labor intensive to make and use.

The cast molding process of the present invention utilizes a multi-part,but preferably in the case of more customary IOLs a four-part,disposable plastic mold system. The first mold part of the subject moldsystem is a female base mold having a positioning wall formed along theperiphery of an interior surface thereof and a molding surface on theinterior surface. The molding surface is comprised of a center cavityused to form one surface of an IOL optic portion, one or more butpreferably two junction cavities and two or more haptic elementcavities. The center cavity is in fluid connection with each junctioncavity. Also, each haptic element cavity is in fluid connection with atleast one junction cavity.

The second mold part of the subject mold system is a center male moldhaving a molding surface on an interior surface comprised of an opticcavity used to form the second surface of the IOL optic portion. Thecenter male mold is sized to be fully received within the positioningwalls of the female base mold and may be shaped to ensure axial androtational alignment.

The third and fourth mold parts of the subject mold system are hapticmolds. Each haptic mold likewise has a molding surface on an interiorsurface comprised of one or more junction cavities and at least onehaptic element cavity. When the haptic molds are placed in aninterlocked relationship with center male mold, junction cavities andhaptic element cavities are in fluid connection with optic cavity.Haptic molds are also male molds sized to be fully received within thepositioning walls of the female base mold and preferably shaped toensure axial and rotational alignment. Each haptic mold is also formedto have material guides or ports extending from the haptic elementcavity and/or junction cavity through to the exterior surface of themold. Optionally, center male mold and haptic molds may be formed as aunitary mold.

The subject preferably four-part mold is used to cast mold a surgicalimplant, preferably an IOL, using two or more dissimilar biocompatiblematerials. An IOL having an optic portion of one preferably moreresilient biocompatible material and haptic elements of a dissimilarpreferably more rigid biocompatible material is produced by filling thebase mold center cavity with the desired more resilient IOL opticmaterial. The center male mold is then inserted into the female basemold allowing excess molding material to pass into one or more overflowreservoirs. During this process, some molding material flows intofluidly connected junction cavities so as to only partially fill thesame. Shields are then positioned over the partially filled junctioncavities and the molding material in the center cavity is polymerizedusing methods of polymerization known to those skilled in the art. Dueto shielding, or any suitable method of protection, the molding materialin the junction cavities is not polymerized. After removing the shields,the haptic molds are then inserted into the female base mold and asecond dissimilar relatively rigid biocompatible molding material isprovided through the material guides or ports to completely fill thejunction cavities and the haptic element cavities. The remainingunpolymerized first molding material and the second molding material arethen polymerized using methods of polymerization known to those skilledin the art. Following polymerization, all three male molds are removedfrom the female mold. The IOL is removed from the female mold throughthe use of solvents or vibration.

Accordingly, it is an object of the present invention to provide a castmolding system to produce IOLs having an optic portion and hapticelements produced from dissimilar biocompatible materials.

Another object of the present invention is to provide a method for castmolding IOLs having an optic portion and haptic elements produced fromdissimilar materials which is less labor intensive.

Another object of the present invention is to provide a method for castmolding IOLs having an optic portion and haptic elements produced fromdissimilar materials with lower production costs.

Another object of the present invention is to provide molds for castmolding IOLs having an optic portion and haptic elements produced fromdissimilar materials.

Still another object of the present invention is to provide a method forcast molding IOLs having an optic portion and haptic elements producedfrom dissimilar materials suitable for high volume production.

These and other objectives and advantages of the present invention, someof which are specifically described and others that are not, will becomeapparent from the detailed description, drawings and claims that followwherein like features are designated by like numerals.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of an intraocular lens having an optic portion andtwo haptic elements;

FIG. 2 is a plan view of an intraocular lens having an optic portion andthree looped haptic elements;

FIG. 3 is a plan view of an intraocular lens having an optic portion andtwo plate haptic elements;

FIG. 4 is an exploded view in perspective of a disposable mold systemfor molding an IOL having an optic portion and haptic elements producedfrom dissimilar materials, constructed in accordance with the teachingsof the present invention;

FIG. 5 is a plan side view of the female base mold of the mold system ofFIG. 4;

FIG. 6 is a cross-sectional side view of the female base mold of FIG. 5taken along lines 6—6;

FIG. 7 is a plan side view of the center male mold of the mold system ofFIG. 4;

FIG. 8 is a plan bottom view of the center male mold of FIG. 7;

FIG. 9 is a plan side view of the haptic mold of the mold system of FIG.4;

FIG. 10 is a cross-sectional side view of the haptic mold of FIG. 9taken along lines 10—10;

FIG. 11 is an exploded view in perspective of a disposable mold systemfor molding an IOL having an optic portion and haptic elements producedfrom dissimilar materials, constructed in accordance with the teachingsof the present invention;

FIG. 12 is a plan side view of the female base mold of the mold systemof FIG. 11;

FIG. 13 is a cross-sectional side view of the female base mold of FIG.12 taken along lines 13—13;

FIG. 14 is a plan side view of the center male mold of the mold systemof FIG. 11;

FIG. 15 is a plan bottom view of the center male mold of FIG. 14;

FIG. 16 is a plan side view of the haptic mold of the mold system ofFIG. 11;

FIG. 17 is a cross-sectional side view of the haptic mold of FIG. 16taken along lines 17—17; and

FIG. 18 is a plan side view of a shield useful with the mold system ofFIG. 4 or FIG. 11.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is a method of cast molding surgical implants,such as most preferably intraocular lenses (IOLs), from dissimilarbiocompatible materials, disposable molds useful for such cast moldingmethod and surgical implants produced using such cast molding method.FIGS. 1 through 3 illustrate various IOLs that may be molded using thecast molding method of the present invention. Various IOLs areillustrated herein for purposes of example only and are not intended tobe in any way limiting to the scope of the present invention. FIG. 1illustrates an IOL 10 having an optic portion 12 and two haptics 18.FIG. 2 illustrates an IOL 10 having an optic portion 12 and three loopedhaptics 18. FIG. 3 illustrates an IOL 10 having an optic portion 12 andtwo plate haptics 18.

The present cast molding method is useful in the manufacture of surgicalimplants, such as IOLs 10 as illustrated in FIGS. 1 through 3, whereinthe optic portion 12 and haptic elements 18 are produced using two ormore dissimilar biocompatible materials. It is desirable to produce IOLs10 from dissimilar materials to optimize optical characteristics of theIOL 10 optic portion 12, optimize support and flexibilitycharacteristics of the IOL 10 haptic elements 18, and, if desired, toalso optimize support and flexibility characteristics of the IOL 10haptic attachment area 13. However, if desired, the subject molds may beused in the manufacture of IOLs 10 having an optic portion 12 and hapticelements 18 produced using the same or similar biocompatible materials.

Suitable biocompatible optic molding materials include but are notlimited to most preferably materials having a refractive index of 1.25or higher and a level of resiliency that enables the material to returnto its original shape after having been folded or compressed in smallincision implantation. Examples of such materials include but are notlimited to silicone polymers, hydrocarbon and fluorocarbon polymers,hydrogels, soft acrylic polymers, polyesters, polyamides, polyurethane,silicone polymers with hydrophilic monomer units, fluorine-containingpolysiloxane elastomers and combinations thereof. The preferred materialfor the production of optic portion 12 due to desirable characteristicsis a hydrogel made from 2-hydroxyethyl methacrylate (HEMA) and6-hydroxyhexyl methacrylate (HOHEXMA), i.e., poly(HEMA-co-HOHEXMA).Suitable haptic molding materials include but are not limited tomaterials capable of providing support without excessive fragility.Examples of such materials include but are not limited to methacrylates,acrylates, more rigid hydrogels, silicone polymers and combinationsthereof. The preferred material for the production of haptic elements 18due to desirable characteristics is polymethyl methacrylate (PMMA).

Materials having characteristics suitable for the manufacture of otherophthalmic implants formed of dissimilar materials utilizing the methodand molds of the present invention become obvious to those skilled inthe art in light of the present disclosure.

The cast molding method or process of the present invention utilizes amulti-part, but preferably a four-part for manageability, disposableplastic mold system 24 as best illustrated in FIG. 4. The first part ofmold system 24 is female base mold 26 having a positioning wall 52 alongperiphery 56 of interior surface 50 and a molding surface 54 comprisedof a center cavity 28, used to form one anterior surface 14 or posteriorsurface 16 of optic portion 12, one or more but preferably two junctioncavities 30 in fluid connection with center cavity 28 and at least onehaptic element cavity 32 in fluid connection with junction cavities 30.Surrounding center cavity 28, junction cavities 30 and haptic elementcavity 32 is extended edge 84 to eliminate material flow between moldsto prevent flash. Base mold 26 is sized as needed according to thearticle to be manufactured using the same. For the manufacture of IOLs10, base mold 26 is approximately 20 to 35 mm but preferablyapproximately 25 to 35 mm in length for ease in handling, approximately10 to 20 mm but preferably approximately 15 to 20 mm in width for easein handling and approximately 10 to 20 mm but preferably 15 to 20 mm inheight for ease of handling. Each of the molding cavities of base mold26 may be sized to be slightly larger in size than the final IOL productdesired to accommodate for material shrinkage, often times as high as 15percent, during polymerization thereof. Alternatively, overflowreservoirs 66 may be shielded from polymerization whereby nonpolymerizedmaterial therein may flow into adjacent cavities upon shrinkage ofpolymerized material in the adjacent cavities and be polymerized.Polymerization of material to form an implant is preferably carried outunder pressure within the range of approximately 50,000 pounds persquare inch at extended edge 84 and edge recess 86 to eliminate cosmeticdefects in the product formed.

The second part of mold system 24 is center male mold 34 having aninterior surface 50 with a molding surface 58 comprised of an opticcavity 60 used to form the second surface, either anterior surface 14 orposterior surface 16 of optic portion 12, surrounded by edge recess 86.Edge recess 86 is sized to accept and work in conjunction with extendededge 84 of female base mold 26. Center male mold 34 is sized to be fullyreceived snugly within positioning walls 52 of female base mold 26 andshaped to interlock for axial and rotational alignment. To ensure axialand rotational alignment, any of a variety of means may be used such asfor example but not limited to providing base mold 26 and center malemold 34 with aligning pins 80 and pin recesses 82 on interior surface 50thereof, providing shape specific forms to base mold 26 and center malemold 34 such as illustrated in FIG. 4 and/or providing base mold 26 andcenter male mold 34 with tab 20 and groove 22 alignment means asillustrated in FIG. 11. For the manufacture of IOLs 10, center male mold34 is approximately 5 to 12 mm but preferably approximately 6 to 10 mmin length to allow optic cavity 60 to be slightly larger than the finaldesired optic diameter, approximately 8 to 18 mm but preferablyapproximately 13 to 18 mm in width for proper fit within positioningwalls 52 and approximately 10 to 20 mm but preferably 15 to 20 mm inheight for ease of handling. As noted above, optic cavity 60 of centermale mold 34 may be sized to be slightly larger in size than the finaloptic portion 12 desired due to material shrinkage during polymerizationthereof.

The third and fourth mold parts of mold system 24 are haptic molds 62.Each haptic mold 62 likewise has an interior surface 50 with moldingsurface 64 comprised of one or more junction cavities 40 and at leastone haptic element cavity 42 in fluid connection with optic cavity 60surrounded by edge recess 86. Haptic molds 62 are male molds sized to befully received within positioning walls 52 of the female base mold 26and shaped to interlock for axial and rotational alignment as describedabove. Haptic molds 62 are also formed to have material guides or ports46 extending from haptic element cavity 42 and/or junction cavity 40through to the exterior surface 48 of the haptic mold 62. For themanufacture of IOLs 10, haptic mold 62 is approximately 14 to 22 mm butpreferably approximately 18 to 24 mm in length to allow proper fitwithin positioning walls 52, approximately 8 to 18 mm but preferablyapproximately 13 to 18 mm in width to allow proper fit withinpositioning walls 52 and approximately 10 to 20 mm but preferably 15 to20 mm in height for ease of handling. As noted above, each cavity ofhaptic mold 62 may be sized to be slightly larger in size than the finalcorresponding product part desired due to material shrinkage duringpolymerization thereof.

Suitable materials from which mold system 24 may be manufactured includefor example but are not limited to polyurethanes, polypropylene,polyvinyl chloride or acrylates. In the case of ultraviolet light curingof the IOL 10 materials, a transparent or translucent material such aspolypropylene is preferred.

The subject preferably four-part mold system 24 is useful to cast moldintraocular implants such as preferably an IOL 10 having an opticportion 12 and haptics 18 preferably manufactured from dissimilarbiocompatible materials. An IOL 10 is cast molded in accordance with thepresent invention by providing a predetermined quantity of a suitableoptic portion 12 molding material into the center cavity 28 of base mold26. The center male mold 34 is then inserted within positioning walls 52of female base mold 26 allowing excess molding material to pass into oneor more overflow reservoirs 66. During this process, some moldingmaterial flows into junction cavities 30. Shields 68 are then placedwithin positioning walls 52 using handles 70 to shield interior surface50 of base mold 26. Base 72 of shield 68 is dimensioned to be the sameas that of interior surface 50 of haptic mold 62 to ensure proper fitwithin positioning walls 52. Shields 68 are preferably fabricated fromthe same material as mold system 24 with the addition of an ultravioletlight absorber such as for example but not limited to2-hydroxy-5-acryloyloxyphenyl-2H-benzotriazoles orvinylsilylalkoxyarylbenzotriazoles. The molding material between centercavity 28 and optic cavity 60 is then polymerized using methods ofpolymerization known to those skilled in the art such as but not limitedto ultraviolet light or heat curing. Due to shields 68, the moldingmaterial in junction cavities 30 is not polymerized. Shields 68 are thenremoved from base mold 26 and haptic molds 62 are then placed withinpositioning walls 52 of female base mold 26. Suitable haptic moldingmaterial is provided through material guides 46 of haptic molds 62 tofill junction cavities 30 and 40 and haptic element cavities 32 and 42with any excess material flowing into reservoir 66. The haptic moldingmaterial is then polymerized using methods of polymerization known tothose skilled in the art such as but not limited to ultraviolet light orheat curing. Following polymerization, all three male molds, i.e., thecenter male mold 34 and both haptic molds 62, are removed from femalebase mold 26. IOL 10 is removed from female base mold 26 through the useof solvents or vibration. IOL 10 is then optionally polished as needed,sterilized and packaged as customary in the art.

As described in detail above, the method of cast molding intraocularimplants such as but not limited to IOLs, the molds suitable for suchcast molding and the IOLs so produced in accordance with the presentinvention provides a relatively inexpensive method of manufacturingimplants produced from two or more dissimilar materials. The presentdescription is provided for purposes of illustration and explanation. Itwill be apparent to those skilled in the art that modifications andchanges may be made to the preferred embodiment described herein withoutdeparting from its scope and spirit.

I claim:
 1. A method for cast molding an ophthalmic implant from two ormore dissimilar materials comprising: filling a center cavity andallowing partial fill of junction cavities of a mold with a firstbiocompatible mate; polymerizing said first biocompatible material insaid center cavity while shielding and not polymerizing said firstbiocompatible material in said junction cavities; filling partiallyfilled junction cavities and remaining cavities of said mold with asecond biocompatible material dissimilar to said first biocompatiblematerial; and polymerizing said first and second biocompatible materialsin said junction cavities and said remaining cavities.
 2. A method forcast molding an intraocular lens from two or more dissimilar materialscomprising: filling a center cavity and allowing partial fill ofjunction cavities of a mold with a first biocompatible material;polymerizing said first biocompatible material in said center cavitywhile shielding and not polymerizing said first biocompatible materialin said junction cavities; filling partially filled junction cavitiesand remaining cavities of said mold with a second biocompatible materialdissimilar to said first biocompatible material; and polymerizing saidfirst and second biocompatible materials in said junction cavities andsaid remaining cavities.
 3. The method of claim 1 or 2 wherein saidfirst biocompatible material is selected from the group consisting ofsilicone polymers, hydrocarbon and fluorocarbon polymers, hydrogels,soft acrylic polymers, polyesters, polyamides, polyurethane, siliconepolymers with hydrophilic monomer units, fluorine-containingpolysiloxane elastomers and combinations thereof.
 4. The method of claim1 or 2 wherein said first biocompatible material is poly(HEMA-co-HOHEXMA) which is made from 2-hydroxyethyl methacrylate (HEMA)and 6-hydroxyhexyl methacrylate (HOHEXMA).
 5. The method of claim 1 or 2wherein said second biocompatible material is selected from the groupconsisting of methacrylates, acrylates, hydrogels, silicone polymers andcombinations thereof.
 6. The method of claim 1 or 2 wherein said secondbiocompatible material is polymethyl methacrylate.
 7. The method ofclaim 1 or 2 wherein said first and second biocompatible materials arepolymerized using ultraviolet light.
 8. The method of claim 1 or 2wherein said first and second biocompatible materials are polymerizedusing heat.
 9. The method of claim 1 or 2 wherein said first and secondbiocompatible materials are both hydrogel materials possessingdissimilar characteristics.
 10. The method of claim 1 or 2 wherein saidmethod includes polishing said ophthalmic implant or intraocular lensfollowing removal from said mold.
 11. The method of claim 1 or 2 whereinsaid method includes sterilizing said ophthalmic implant or intraocularlens following removal from said mold.
 12. An intraocular implantmanufactured by the method of claim
 1. 13. An intraocular lensmanufactured by the method of claim 1 or
 2. 14. An intraocular lens withtwo or more haptics manufactured by the method of claim 1 or
 2. 15. Anintraocular lens with two or more looped haptics manufactured by themethod of claim 1 or
 2. 16. An intraocular lens with two or more platehaptics manufactured by the method of claim 1 or 2.